VDE-AR-N 4105:2018, EN50549-1:2019,
VFR2019, IEC/EN 62109-1/-2, IEC/EN
61000-3-2/-3, IEC/EN-61000-6-1/-2/-3/-4
Appendix
Determining the line reserve
The PI Photovoltaic Institute Berlin in cooperation with the German Society for Solar
Energy (DGS), the University of Applied Sciences (HTW) Berlin have worked out in a
study that it is possible to feed in up to 2.6 amps (approx. 630W, equivalent to 2 solar
modules) with plug-in solar devices in every household with circuit breakers without
any safety concerns, without having to make any changes to the house electrics.
However, there may be a deviation from the applicable standard for line loading. We
have described how to comply with the requirements of the standard and how to test
the line in this appendix. If mini solar systems feed into the existing final circuit, the
current load on individual cable sections may exceed the designed standard size. To
prevent overloading of the cables in the household, they are protected by a line circuit
breaker (LSS). This switches off automatically as soon as an overload occurs. As a
rule, several sockets and consumers are protected by a common line protection. Due
to the additional power of the mini solar system, the currents from the utility grid and
the mini solar system can now add up. However, the currents are not detected by the
line circuit breaker, so theoretically an overload can occur. You can use the following
formula to determine whether the existing line with your circuit breaker is sufficiently
dimensioned:
Iz indicates the current carrying capacity of the line, which should be greater than the
sum of the rated current of the protective device (circuit breaker in amperes) and the
generating equipment (power in amperes). Both Iz and Ig can be found in the following
table for the example application below.
Iz = In + Ig
Iz Permissible current carrying capacity of the line
In Rated current of the protective device (circuit breaker)
Ig rated current of the power generation system
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